Correlated probabilistic analysis of the excavation times and costs in tunneling

A new calculation procedure, called PACT, is presented for the probabilistic analysis of the construction times and costs of tunneling. Once the tunnel strength is divided into homogeneous sections, it is necessary that all the operations on the critical path and the quantities of materials used for each of the previously identified classes are described in analytical terms. A selection is made from the parameters that show a certain degree of uncertainty. A standard deviation of the probabilistic distribution is defined for these parameters. The final result is the identification of the probability ellipses with a certain degree of reliability. The ellipses define the total field of variability of the construction times and costs of the tunneling. The procedure was successfully applied to the pilot tunnel of the Italian section of a 13-km long alpine tunnel. It proved possible to obtain the joined probabilistic description of the times and costs as a result of the evaluation of 95 elementary parameters, 25 of which are considered probabilistic ones because of the uncertainties of their estimation.